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Weight gain and remaining overweight were independently associated with a significantly increased risk of onychomycosis, even after controlling for potential confounders, according to data from almost nine million Korean adults.

Note that while an association between high body mass index (BMI) and increased risk of onychomycosis has been demonstrated in previous studies, the impact of weight gain on the risk has not been previously investigated.

Weight gain was independently associated with a significantly increased risk of onychomycosis, even after controlling for potential confounders, researchers found.

Analysis of data from approximately nine million patients in the Korean national insurance system showed that those who gained weight (hazard ratio [HR] 1.09) over a period of 4 years and who remained overweight afterward (HR 1.18) had a significantly higher risk of developing the fungus than those who maintained a normal weight.

"An increase in [body mass index (BMI)] was positively associated with an increased incidence of onychomycosis," Ji Hyun Lee, MD, PhD, of Seoul St. Mary's Hospital and The Catholic University of Korea, and colleagues reported in a research letter in the Journal of the American Academy of Dermatology.

A statistically significant increase in the risk for onychomycosis was also observed in patients who maintained a BMI ≥30 during a 4-year period between 2005 and 2012 (Ptrend <0.0001), the analysis revealed.

The risk factors for onychomycosis include age as well as comorbidities such as diabetes, an immuno-compromised state, tinea pedis, and peripheral vascular disease, the study authors noted, adding that while an association between high BMI and increased risk of onychomycosis has been demonstrated in previous studies, the impact of weight gain on the risk has not been investigated.

Asked for her perspective, Marie Jhin, MD, an American Academy of Dermatology (AAD) expert in San Francisco and San Carlos, CA, who was not affiliated with the study, said the findings are not particularly helpful for the practicing dermatologist: "By the time a patient comes to us with onychomycosis, we are there to discuss treatment and not consult about weight," Jhin told MedPage Today.

However, another AAD expert not affiliated with the study, Shari Lipner, MD, PhD, of Weill Cornell Medicine in New York City, said the findings are clinically relevant because they suggest that primary care doctors as well as podiatrists and dermatologists should be screening overweight patients for onychomycosis.

"This new data is interesting and relevant, but further prospective trials are needed to determine its significance," she told MedPage Today.

Limitations of the study, she added, include the fact that the study was retrospective and that only Korean patients and adults were included.

For the study, Lee and colleagues analyzed data on 8,837,719 patients older than age 20, dividing the study population into four groups:

Normal weight (BMI<25 at baseline and 4 years later)

Weight gain (BMI <25 at baseline and ≥25 after 4 years)

Weight loss (BMI ≥25 at baseline and <25 after 4 years)

Overweight (BMI ≥25 at baseline and 4 years later)

After the researchers adjusted for potential confounders, the analysis showed that the incidence rate of onychomycosis in patients who maintained a BMI ≥30 from baseline until the end of the study was 29.7 per 1,000 population. By comparison, the lowest estimated incidence rate -- 12.5 per 1,000 population -- was seen in patients with a BMI <18.5.

In 612,172 patients who maintained a BMI <25 for 4 years, the incidence rate of onychomycosis was 21.04 per 1,000 population, while in the 318,854 individuals who maintained a BMI ≥25, it was 28.12 per 1,000 population.

The prevention and/or management of onychomycosis in patients who are overweight or who gain weight can present several clinical challenges, Lipner noted. Since patients may already be taking medication for comorbidities, potential drug interactions need to be checked before starting oral anti-fungal therapy.

In addition, since obesity is also associated with an increased risk of liver and kidney disease, more frequent blood monitoring will be required than in patients of normal weight. "Patients who are significantly overweight may have trouble applying topical antifungal medications to their toenails, thus interfering with compliance and efficacy," Lipner pointed out.

Early treatment of onychomycosis is key, particularly in patients with immunological disorders, peripheral vascular disease, or diabetes, said Meghan Feely, MD, an AAD expert in New York City, who was also not affiliated with the study.

"It would be of interest to study this topic across a broad demographic, controlling for potential co-founders such as immunological disorders and peripheral vascular disease," she told MedPage Today.

Onychomycosis may also be associated with psoriasis, hyperhidrosis, and nail trauma, Feely warned, explaining that onychomycosis can increase the risk of sores developing on the feet, leading to infection and increased morbidity. In these cases, treatment is often less successful, and there is a higher rate of recurrence.

Although systemic antifungal therapy may be contraindicated in patients with heart disease or renal or liver impairment, or in those with potential drug interactions, the mycotic cure rate is lower with topical versus systemic treatment, Feely added.

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